The transformation of a normal cell to a cancer cell by viruses or carcinogens is often accompanied by dramatic changes in cell morphology. These changes seem to be mediated by changes in the cytoskeleton, particularly in the cytoplasmic microtubules and microfilaments. Very little is known about the molecular biology of these supramolecular structures, particularly about the cellular factors which regulate the time and location of their assembly. The objectives of this research are: (1) characterization of proteins which positively regulate microtubule assembly using immunofluorescent, electronmicroscopic and biochemical methods. We are particularly interested in the possible role of phosphorylation of such tubulin assembly proteins by protein kinases in modulating their function. We will attempt to determine changes in their levels and state of activity (modification) during in vitro transformation of cultured fibroblasts; (2) isolation and characterization of a new class of potential regulatory molecules (proteins, peptides): "tubulin endorphins" which compete with colchicine for binding to tubulin and appear to be the physiological species which interacts with this site on microtubules. At least one of these compounds negatively regulates microtubule assembly. We will investigate where changes in their activity occur during transformation as a possible way of causing cytoskeletal disorganization; (3) identification of transformation specific proteins which may alter microtubule assembly by binding to tubulin.